Electronic devices, such as palm computers, digital cameras and cellular telephones, are becoming more compact and miniature, even as they incorporate more sophisticated data processing and storage circuitry. Moreover, types of digital communication other than text are becoming much more common, such as video, audio and graphics, requiring massive amounts of data to convey the complex information inherent therein. These developments have created an enormous demand for new storage technologies that are capable of handling more complex data at a lower cost and in a much more compact package. Efforts are now underway to adapt technology to enable the storage of data on scale of nanometers to tens of nanometers, sometimes referred to as atomic resolution storage (ARS).
Several challenges arise in attempting to store data at the ARS level. On that scale, reading and writing data by electron beams or by mechanically detecting data pits on the recording media are increasingly delicate operations much more likely to be affected by error. Such data error can arise from stray electrons, atoms or molecules, extraneous noise and straying from the center of a data track.
In some prior art data recording and detection systems, data is written along recording tracks formed on the data-recording layer using data pits. A signal is detected having an amplitude representing the depth of data pits. If the probe tip passed through the center of the data pit, adequate detection could be achieved. However, any track offsets during detection caused the tip to pass over the edge of a pit, so that the amplitude was severely reduced. The result is poor data recovery error rates or extreme servo track following constraints on the system.
Some techniques have been developed in optical data disc systems to improve detection. In one such system, U.S. Pat. No. 5,414,689 (Maeda et al), a signal is generated and differentiated twice to find a zero crossing indicative of a pit characteristic. The first differentiated signal is utilized to qualify the zero crossing of the second order signal. Such a detecting system is too sensitive to low frequency noise found in an ARS system.
Data detection on the level of ARS technology require advanced but relatively simple techniques. The ARS data may be recorded by forming miniature pits or other types of data locations along extremely narrow and crowded multiple recording tracks. In ARS technology, the data storage and recording system is so small that it is very difficult to maintain a mechanical tracking device directly on the centers of the data pits or locations. For example, in such ARS systems, the interval between adjacent recording tracks may be 40-50 nm with only 5-7 nm of tracking error. The data pits or locations may be only about 10-20 nm deep and 35-40 nm in diameter and separated along the track by only a space of 35-40 nm. Thus, a reading that is even slightly off-track can result in inconclusive sensing.
The compact nature of ARS technology also leads to extreme noise problems. To promote precision at the ARS level, mechanical sensing probes may be used to ride along the surface of the recording media, in order to detect data pits or other types of data locations more readily. However, any discontinuities or uneven surface may cause substantial false pit sensing or “media noise.” The presence of significant electronic and media noise along with a rapid fall-off of signal levels as the pits are read off-center of a track make ARS data recovery difficult in such a data detection system.